﻿Vol. 66.] PULAU UBIN AND PULATT NANAS. 427 



Dark Masses in the Microgranite of the South Quarry. 



In the microgranite of the South Quarry, a few ill-defined patches 

 -of dark rock occur, which are of interest in that they show a 

 resemblance to the porphyry exposed behind the North Quarry. 

 Slides prepared from these dark masses show that the clear minerals 

 consist of quartz (sometimes interstitial between felspar crystals), 

 orthoclase and plagioclase, which occasionally form phenocrysts, and 

 micropegmatite. The dark minerals are green hornblende, in ragged 

 flakes and sometimes in spongy masses (like those in the porpbyry), 

 monoclinic pyroxene, biotite, sphene, and magnetite. 



This concludes the description of thePulau Ubin rocks, a description 

 that is far from complete, but emphasizes, I hope, the salient points. 

 Before discussing their relations, I must pass to the Pulau Nanas 

 tuifs and the included granite fragments. 



III. Ptjlatj Nanas. 



One of the important features in the structural geology of 

 Pahang, the largest and least known of the Federated Malay 

 States, has proved to be a widespread series of volcanic rocks of 

 considerable antiquity. 1 These vary in composition, and it is not 

 yet known whether a number of ' greenstones ' should be included 

 in the group or not. For the most part, however, the series con- 

 sists of dacites, with ashes of corresponding composition. These 

 volcanic rocks, which I have named the PahangYolcanic Series, 

 are interbedded with calcareous rocks (the E-aub Series) containing 

 a few organisms referred to the Carboniferous and Permo- Carbo- 

 niferous, and they are evidence of eruptions over a large area of 

 the sea-floor in those times. A characteristic feature of the ashes 

 is the inclusion of fragments of chert and carbonaceous shale ; 

 both ashes and lavas are sometimes found to be sheared, and to 

 contain secondary minerals due to contact-metamorphism caused by 

 the tin-bearing granite. 



The general strike of the Haub Series and the Pahang Volcanic 

 Series is such that they may be expected to extend into Johore, 

 and therefore it is not surprising to find that Pulau Nanas consists 

 entirely of ashes and lavas closely resembling some of those in the 

 Pahang Volcanic Series. They are dacites and dacite-tuff s, and 

 the influence of the neighbouring granite of Pulau Ubin is shown 

 by their hardness, as also by the large development of secondary 

 biotite and hornblende. In the tuffs I have found one or two 

 small pebbles that appear to be altered chert, with very minute 



1 These were described in my ' Report of Progress : Sept. 1903-Jan. 1907 ' 

 (Federated Malay States) Kuala Lumpur, pp. 9-11. 



2g 2 



